The invention relates to a motor vehicle, in particular a motor vehicle with a continuously variable transmission, as well as a method of operating the motor vehicle.
Motor vehicles, including those with a continuously variable transmission, belong to the known state of the art.
From DE 195 46 293 A1, a continuously variable transmission is known that has two pairs of conical disks, each pair comprising a fixed conical disk and, arranged to face the latter, a movable conical disk. A torque is transmitted from one pair of conical disks to the other by means of a chain. Corresponding to the position of the movable conical disks in their respective pairs, different transmission ratios can be set in a continuous range without steps. To hold the position of the chain at a given transmission ratio, or to change the transmission ratio, there is an arrangement of two valve devices connected to the transmission through hydraulic conduits. A first valve device, the ratio-control valve, has seven connector terminals, three of which lead to an oil sump. Connected to a further terminal is a pressure-supply conduit. The pressure that exists in the latter conduit is also communicated to a connector terminal of the second valve device, which has five terminals. The first valve device is controlled by applying to one of the faces of a piston guided inside a cylinder an amount of pressure that is adjustable by means of a proportional valve. Each of two further connector terminals of the ratio-control valve leads to a respective pressure chamber, where one of the two pressure chambers is arranged at the first disk pair and the other is arranged at the second disk pair. From the two further connector terminals, a return conduit branches off towards the second valve device. A connector terminal that is arranged at the axially directed end surface of the second valve device communicates with a pressure supply conduit. Further connected to the second valve device is a conduit that divides into branches outside of the valve device, one branch leading to the first disk pair and one branch leading to the second disk pair for maintaining a previously set level of the transmission ratio.
Each of the two valve devices comprises one pre-tensioning spring. The spring of the second valve device, in particular, has the function of increasing the pressure that is returned from the first valve device by an amount corresponding to the spring force, so that the pressure in the pressure supply conduit is always increased by an amount corresponding to the spring force. This assures that the pressure in the pressure supply conduit is always sufficient for changing the positions of the disk pairs.
The motor vehicle of the foregoing description, which has a continuously variable transmission that is controllable through a hydraulic system, has been practically proven. The pressure return, particularly with the addition of the spring, as well as the comparator device that constantly compares the comparative pressures supplied to the disk pairs, ensure that the pressure in the supply conduit, i.e., on the side of the pressure source, can always be relied on to be sufficient for controlling the transmission.
Nevertheless, there is a desire for improvements, particularly with respect to the space required by the hydraulic valve devices. Also, a more cost-effective design configuration based on a smaller number of individual components would be desirable.
Therefore, the present invention has the object of providing a motor vehicle with a continuously variable transmission as well as a method of operating the motor vehicle whereby the amount of space required for the controls of a continuously variable transmission is reduced, the manufacturing cost of the motor vehicle is lowered, and assembly times are shortened, while at the same time a high level of operating safety and an uncomplicated design configuration are achieved.
In accordance with the invention, the foregoing objective is met by providing a motor vehicle with at least one continuously variable transmission and at least one hydraulic device for controlling a transmission ratio change and for holding a set transmission ratio at a fixed level. The term xe2x80x9cholding a set transmission ratio at a fixed levelxe2x80x9d means in particular that an unintentional change of the transmission ratio, which may be inherent in the design or associated with a static or dynamic behavior of the transmission, is prevented. In accordance with the invention, the hydraulic device in particular comprises a valve device with at least one connector terminal for a hydraulic conduit by which the transmission ratio can be changed within a continuous range, i.e., without steps. In particular, this means that a transmission ratio change is effected by an overpressure, an underpressure, or a pressure-free condition in a hydraulic line connected to a terminal of the valve device. As a particular feature of the invention, a valve is provided for switching from the state of holding to the state of changing the transmission ratio. The terminals at the transmission-oriented side of the valve can be or are connected to conduits for supplying the respective amounts of pressure required for changing or maintaining the transmission ratio.
In comparison to the arrangement proposed in DE 195 46 293 A1, the inventive concept of providing a single valve device offers the advantage of a space-saving configuration of the hydraulic controls of a transmission. In addition, the invention saves several components such as, e.g., valve cylinders, valve pistons, or connecting conduits between valves. Furthermore, the invention increases the operational safety of a control device for a motor vehicle transmission and thus of the motor vehicle itself.
The objective of the invention is met further by equipping a motor vehicle with at least one continuously variable transmission comprising at least two pairs of conical disks for receiving an endless flexible torque-transmitting device. At least one of the conical disk pairs includes two elements that are movable in relation to each other in the axial direction, particularly the two conical disks themselves. For example, one conical disk may have a fixed attachment or other fixed relation to a shaft or similar element while the second conical disk may, e.g., have a movable seat on the shaft. By changing the axial distance of the two conical disks, a location where the mutually facing surfaces of two conical disks have a given distance from each other will be caused to move radially in or out to a corresponding extent. The given distance is occupied in particular by an endless flexible torque-transmitting device of a defined width. As a result, the radial distance of the endless flexible torque-transmitting device from the central axis of the conical disk pair is selectable, preferably at each of the conical disk pairs.
At least one, preferably two, and with particular preference all of the conical disk pairs are provided with means for applying hydraulic pressure to at least one side. This application of hydraulic pressure can, e.g., ensure that a currently existing transmission ratio is being held at a fixed level, unless at the particular instant the control device is directing a change of the transmission ratio. The control can, e.g., function in such a way that essentially one and the same pressure is applied to both conical disk pairs. However, the same function of maintaining the transmission ratio can also be realized by applying different amounts of pressure to the conical disk pairs, if the holding pressure at the respective conical disk pair depends on an operating parameter such as, e.g., the transmission ratio.
In accordance with a first preferred embodiment of the invention, a pressure differential between the conical disk pairs can be generated by arranging a throttle valve in a connecting conduit between pressure chambers of which at least one is located at a first conical disk pair and at least one other is located at a second conical disk pair.
In accordance with a further preferred embodiment of the invention the same kind of pressure differential between the conical disk pairs can be achieved through an arrangement where the pressure chambers at the conical disk pairs are connected by a hydraulic line that contains the same amount of pressure throughout and where the required offset pressure is provided by a second, additional pressure supply.
The preferred arrangement of changing or maintaining the transmission ratio is by way of a dual-piston principle. As a particular characteristic of this arrangement, a first chamber located at a first conical disk pair is connected to a second chamber at a second conical disk pair by a hydraulic line. An essentially constant pressure is supplied to the hydraulic line, providing at least a base amount of pressure for the maintaining function. A preferred configuration comprises an essentially parallel and/or serial arrangement with, in particular, a third chamber acting on the first conical disk pair and a fourth chamber acting on the second conical disk pair. The preferred arrangement for the fist and third chambers and also for the second and fourth chambers is such that, with a base pressure being supplied by the first and third chambers, the change of the transmission ratio occurs through the second and fourth chambers. It is particularly preferred if the second and fourth chambers provide a certain pressure differential, which is superimposed on the constant and equal pressure level of the first and third chambers.
According to the invention it is particularly preferred that the lines that supply hydraulic pressure to the conical disk pairs, particularly for maintaining or changing a transmission ratio, lead into the same valve device. It is also possible for the aforementioned hydraulic lines to contain valve devices. However, it is particularly preferred, if essentially no valve devices are arranged in these hydraulic lines. Particularly preferred is a valve device that can be characterized as a piston-cylinder valve device with a single valve cylinder.
The objective of the invention is met further by equipping a motor vehicle with a continuously variable transmission and, adjacent to the latter, at least one hydraulic device for the control of the transmission. The term xe2x80x9ccontrolxe2x80x9d encompasses the two particular meanings of, respectively, maintaining a set transmission ratio at a fixed level and of changing a transmission ratio from one level to another. Preferably, the hydraulic device comprises at least one pump and at least one valve device for controlling the transmission, the valve device being arranged between the pump and the transmission. In accordance with the invention, the hydraulic control lines that lead into the transmission and, at least part of the time, contain an overpressure supplied by the pump are connected, particularly through a direct serial connection, to the same valve device. A valve device in this context means a piston-cylinder device comprising preferably a single and, in particular, continuous cylinder.
Particularly preferred is a motor vehicle with at least one continuously variable transmission that is controllable by means of a hydraulic device, the latter operating in accordance with the dual-piston principle. The inventive concept provides that all hydraulic control signals for controlling the transmission originate from the same valve device.
Further preferred is a motor vehicle with a continuously variable transmission controlled by at least one hydraulic device, the latter comprising at least a pump and a valve device for controlling the transmission. The arrangement is configured according to a dual-piston principle. The inventive concept provides for the transmission to have two conical disk pairs, each of which has one fixed and one movably mounted conical disk. The two movable conical disks are energized by a first and second hydraulic chamber, respectively, so that an endless flexible torque-transmitting device such as, e.g., a chain essentially maintains its spatial relationship to the conical disk pairs and, as a result, the transmission ratio remains essentially constant. A third and fourth hydraulic chamber arranged, respectively, at the first and second conical disk pair allow, e.g., an additional amount of pressure to be applied to one of the conical disk pairs or, more specifically, to one of the movably mounted conical disks. For example, the additional amount of pressure can be applied for the purpose of holding the conical disk in the case where the first and second chambers are to be held under a constant pressure, but the magnitude of the constant pressure is insufficient for maintaining the transmission ratio at its level. Further, as an example, it is possible to change the transmission ratio through the third and fourth chambers. For example, pressurizing the third chamber may change the transmission in one direction while pressurizing the fourth chamber may serve to change the transmission in the opposite direction. Preferably in this arrangement, the non-pressurized chamber is set into a pressure-free condition. Particularly preferred is an arrangement where all of the aforementioned functions are controlled by a single valve device. Preferably, the valve device receives a control signal, e.g., a hydraulic signal, but not excluding electrical or magnetic control signals as other preferred possibilities.
Thus, the invention particularly allows the respective functions of changing and maintaining a transmission ratio to be performed by a single valve device that is arranged aheadxe2x80x94with preference immediately aheadxe2x80x94of the transmission. As a particular advantage of the invention, an arrangement of valves located immediately ahead of the transmission for the hydraulic control of the latter can be combined into a single valve. This saves, e.g., a second valve that is proposed in known prior-art arrangements. Consequently, it becomes unnecessary to provide a pressure return between two valve devices to ensure that the pressure level is always sufficient for changing the transmission ratio.
A particularly preferred motor vehicle according to the invention has a continuously variable transmission as well as an endless flexible torque-transmitting device for transmitting torque between different components of the transmission, particularly between at least two conical disk pairs. To control the transmission, the inventive concept particularly includes a hydraulic device with a valve device that has at least two connector terminals, preferably three connector terminals. The inventive concept provides for at least one, and preferably only one, of these connector terminals to supply pressure, at least part of the time, for holding the endless flexible torque-transmitting device in place. The inventive concept further provides for at least one, preferably at least two, but with particular preference exactly two of the connector terminals to supply pressure, at least part of the time, for changing the ratio of the transmission.
A preferred motor vehicle has a continuously variable transmission. An endless flexible torque-transmitting device, particularly in the form of a chain, serves for transmitting torque between different components of the transmission. The transmission components are, in particular, at least two pairs of conical disks. Through a hydraulic device comprising at least two, but preferably three, connector terminals, it is possible to apply pressure to the transmission, i.e., particularly to the conical disk pairs, through an arrangement where the amounts of pressure are cumulative at least part of the time, so that the sum of the pressures is applied to the respective conical disk or disk pair or to the transmission in general. The at least two, but preferably three, connector terminals have the particular purpose of receiving hydraulic lines for supplying pressure to the transmission. The hydraulic lines transmit pressure to hydraulic chambers. The introduction of pressure into the chambers is configured so that in two places, particularly at the two conical disk pairs, at least two pressuresxe2x80x94occurring particularly in two different chambersxe2x80x94act at least part of the time in an additive mode as a xe2x80x9csummation pressurexe2x80x9d.
This permits, e.g., to hold the pressure in the system at a relatively low level.
In accordance with a particularly preferred embodiment of the invention, a motor vehicle is provided with at least one continuously variable transmission as well as a hydraulic device for controlling the transmission. The hydraulic device comprises at least one valve device with a piston device as well as a cylinder device. In particular, the piston device and the cylinder device, in at least one position in relation to each other, form a chamber that contains an essentially uniform pressure. The chamber is delimited by surface areas which, at least in part, have projected images in a plane that faces in the direction of the piston displacement path. A part of the surface areas with this property belong to the piston device, and a further differentiation is possible between surface areas where an applied pressure will cause the piston to move one way and surface areas where an applied pressure will cause the piston to move the opposite way. Furthermore, the so differentiated surface areas are of different size.
In accordance with a further preferred embodiment of the invention, a motor vehicle is provided with a continuously variable transmission. For the control of the transmission, i.e., particularly for maintaining or changing a set transmission ratio, the motor vehicle is provided with a hydraulic device that comprises a valve device in a serial operating arrangement.
The valve device comprises less than 12 connector terminals, with an increasing degree of preference for numbers of less than 11, 10 or 9, and particularly less than 8, 6, or 5, also with particular preference for numbers between 10 and 5, especially between 9 and 6, and a particularly high degree of preference for exactly 8 connector terminals.
In the context of the invention, the particular meaning of the term xe2x80x9cserial operating arrangementxe2x80x9d of the valve device is that between the pump and the transmission there is an area of the hydraulic system comprising in principle an arbitrary number of hydraulic connecting lines, all of which terminate at the same valve device and, in particular, that in the flow path between the pump and the transmission, there is no hydraulic line that bypasses the one valve device in parallel so that it would lie in the flow path between the pump and the transmission without being connected to the valve device.
A particularly preferred embodiment of the invention comprises provisions whereby in a valve device for controlling a continuously variable transmission of a motor vehicle, and particularly in a serially arranged valve device, the pressure on the side of the pressure source or pump can be throttled while, at the same time, assurance is provided that at least part of the time, but preferably in all situations where a transmission ratio change is intended, the pressure acting on the transmission is sufficient to perform the intended ratio change. Thus, the inventive concept provides in particular that, in a valve device for maintaining or changing a set transmission ratio, the pressure can be throttled, the valve device being in particular a serially arranged valve device comprising preferably less than 3, but with particular preference one and only one piston.
In accordance with a particularly preferred embodiment of the invention, the control device for controlling a continuously variable transmission is configured to adapt itself to the demand for pressure, so that in particular the energizing pressure for changing the transmission can be adjusted to the required pressure level. The demand-adapting control device assures in particular that the system pressure level remains essentially low but is always sufficient to perform the transmission ratio change as required in any given situation. The control is performed, for example, through a hydraulic system that operates according to a dual-piston principle that makes use of the fact that the pressure levels existing in different chambers or conduits are additive in generating a resultant pressure in a way where the resultant summation pressure does not have to be actually present in a separate chamber or conduit.
According to the invention, a control device for controlling the transmission, particularly an at least in part hydraulically based control device, comprises at least one device for setting a target value, at least one device for generating the targeted pressure, at least one device for comparing a target value with an actual value, and at least one device for correcting the actual value if the actual value and the target value are different from each other. Preferably, the device for setting the target value generates a signal that can, e.g., also be in the form of a pressure level. The preferred mode of functioning is that a valve device takes on a condition corresponding to the given target value, so that the controlled parameter, particularly a pressure level, takes on a certain actual value. The invention provides in particular that the process of making an actual value conform to a target is performed within a single valve device, particularly a valve device with fewer than three pistons and one cylinder. With special preference, the process is performed within a valve with one piston and one cylinder.
According to a particularly preferred embodiment of the invention, the control device for controlling a continuously variable transmission of a motor vehicle, particularly a control device configured at least in part as a hydraulic device, comprises a valve device in the form of a piston-cylinder device. Within the latter, chambers are formed at least part of the time in an arrangement where the axially projected wall portions that belong to the piston device are of unequal size relative to the directions of the two opposite piston ends. As a result, with an equal amount of pressure acting on both sides, there will be a resultant force on the piston, provided there are no other forces acting on the piston.
In order of preference, the continuously variable transmission comprises at least one, better two, sets of disks, each set consisting of at least two disks with a contact area for receiving an endless flexible torque-transmitting device. In the area for receiving an endless flexible torque-transmitting device, the axial distance between the disk changes as a function of the radius. Preferably, the respective portions of the disks are given a conical shape. Other cross-sectional shapes such as, e.g., segments of circles are likewise within the range of preferred configurations. As a preferred concept according to the invention, the valve device has for each disk set (particularly for disk sets of the kind just described) at least one chamber with different-sized wall areas in the two piston-travel directions so that, with no other forces acting on the piston and with a constant amount of pressure within the chamber, there will be a resultant force on the piston.
Preferably, the valve device is configured as a piston-cylinder unit in which the cylinder device has a continuous, essentially uninterrupted interior space. With preference, the interior space serves to accommodate the piston device.
In accordance with a particularly preferred embodiment of the invention, the valve device, meaning the piston-cylinder unit, comprises fewer than three, with particular preference fewer than two, pistons that are movable in relation to each other. Preferably, the valve device is configured as a linear displacement valve device. With special preference, the valve device is configured with a pressure return.
In accordance with a particularly preferred embodiment of the invention, the valve device that serves in particular to change the transmission ratio, has at least one channel that runs inside the piston at least partially in the axial direction or has at least components running along an axial direction.
It is also preferred if at least one of the channels inside the piston can accommodate an internal slide, particularly one with an essentially fixed arrangement in relation to the cylinder device.
A particularly preferred embodiment of a motor vehicle in accordance with the invention comprises within a valve device for controlling a continuously variable transmission at least one channel running at least partially in an axial direction inside the piston and at least one opening or channel extending from the inside channel towards the outside surface of the piston. It is preferable to have two such openings or channels from the interior of the piston to the outside. With particular preference, there are two such openings at different axial positions on the piston. A preferred embodiment of an inventive valve device for controlling a continuously variable transmission of a motor vehicle comprises at least one hydraulic OR-gate, where the particular function of the valve device is to change and maintain the transmission ratio. Further, in an especially preferred version, this kind of valve device does not have nor require a hydraulic OR-gate.
In accordance with a particularly preferred embodiment of the invention, the valve device has at least one, preferably two, connector terminals for a connecting conduit to a pump.
It is particularly preferred if the valve device for controlling the continuously variable transmission comprises at least one connector terminal for a connection to a torque sensor.
With preference, the valve device has at least one connector terminal for a conduit to generate a compressive contact force between at least one disk pair and an endless flexible torque-transmitting device. In particular, the compressive contact force serves to maintain the transmission ratio at a set level.
In accordance with a particularly preferred embodiment of the invention, the valve device has at least one connector terminal for a hydraulic connection to at least one proportional valve.
With preference, the valve device has at least one connector terminal for a means of conducting the energizing pressure to at least a first and/or at least a second set of disks of the hydraulically controlled transmission.
It is a particularly preferred feature, that for a change in the direction towards xe2x80x9coverdrivexe2x80x9d, pressure can be applied to a first set of disks through a connecting conduit and for a change in the direction towards xe2x80x9cunderdrivexe2x80x9d, pressure can be applied to another disk set. Preferably, the possibility is provided to allow the respective pressures for changing the transmission ratio towards xe2x80x9cunderdrivexe2x80x9d and xe2x80x9coverdrivexe2x80x9d to be applied through a conduit that is connected to a single connector terminal of the valve device. However, first preference is given to a configuration in which separate connector terminals for pressure conduits are provided both for a change towards xe2x80x9coverdrivexe2x80x9d as well as for a change towards xe2x80x9cunderdrivexe2x80x9d. In the latter case, the disk sets that are not subjected to a change-energizing pressure at a particular moment are preferably put into a pressure-free state.
In accordance with a particularly preferred embodiment of the invention, the valve device can perform or can be controlled to perform the function of maintaining the transmission ratio of the disk sets of the transmission at a set level as well as the function of setting the transmission ratio to a new level. The valve device through which the two functions are controlled has fewer than twelve, preferably fewer than nine, and with particular preference fewer than eight connector terminals.
In a particularly preferred embodiment, the valve device is configured as a piston-cylinder device wherein the valve device is spring-biased in at least one position, preferably by a compression spring, with a lesser degree of preference given to a tensile spring. In accordance with a particularly preferred embodiment of the invention, a spring force holds the piston device in one end position of the piston.
Preferably, at least one end stop is provided for the purpose of limiting piston travel or, in other words, to limit the piston displacement in the cylinder device. With preference, the end stop is provided between the end positions of the cylinder device. With particular preference, an end stop of this kind extends at least partially from the inner surface of the cylinder device towards the interior of the cylinder, Further, as a preferred feature, the valve device comprises a throttling element of preferably variable throttle cross-section that serves to throttle the pressure supplied by the pressure source or pump if the supplied pressure exceeds a preset level.
In accordance with a particularly preferred embodiment of the invention, a valve device is provided for changing the transmission ratio of a continuously variable transmission as well as for maintaining the transmission ratio at a set level. The valve device serves to apply the change-energizing pressure as well as the ratio-maintaining pressure. Between this valve device and the transmission, the preferred arrangement is to have no other settable control valve device.
It is further preferred if between the valve device and the continuously variable transmission, there is a connecting conduit that opens into the pressure chamber of a torque sensor. It is preferred to have no other settable valve device between the valve device and the point of entry into the torque sensor chamber, and it is particularly preferred to have no valve device of any kind. With strong preference, there is likewise no settable valve device arranged in the other connecting conduits between the valve device and the transmission, but the strongest preference is for no valve device of any kind.
In accordance with a particularly preferred embodiment of the invention, the valve device is configured as a piston-cylinder device wherein pressure can be applied to at last one of the axially facing surfaces of the piston device. It is also within the range of design possibilities to provide means for applying pressure to both of the axially facing surfaces of the piston device.
In accordance with a highly preferred embodiment of the invention, the valve device has at least one connector terminal for a valve-control conduit that is at least part of the time supplied with a valve-control pressure, particularly with a settable pressure that represents a target value for the amount of displacement of the valve device.
In accordance with a particularly preferred embodiment of the invention, the piston device of the valve device, e.g., in the configuration as described above, comprises a hollow interior space to accommodate an internal slide in an arrangement where the frontal end surface of the slide makes up at least part of the difference in surface area that produces a net resultant force when pressure is applied to a chamber.
Particularly preferred is an arrangement in which an equilibrium of the forces in the travel direction of the piston establishes itself at all times between a force that is due to the presence of an internal slide, a spring force acting on the piston device, a valve-control force, as well as an (additional) force caused by the difference in the projected surface areas inside a chamber of the piston device.
A valve-control force, in this particular context, can be defined as a force that occurs as a consequence of a change-energizing pressure that has been applied to the piston device.
In a particularly preferred embodiment of the invention, a valve device which, with strong preference, includes a ring channel designed for this purpose, allows a connection to be established between a pressure-supplying terminal and a connecting terminal for energizing a change of the transmission ratio. It is particularly preferred if the fluid streaming at least in part from the pressure-supplying terminal through the valve device towards the conduit for energizing the transmission-ratio change passes through or is held at zero velocity in a chamber of the valve device and if the wall portions of the chamber that belong to the piston device have different projected surface areas in the two opposite directions of piston displacement travel.
As another preferred feature of the invention, it is further to be noted that the fluid-flow connection from the pressure-supply through the valve device to the change-energizing conduit of the transmission can also be interrupted at least part of the time without causing a change of the chamber geometry.
In a particularly preferred embodiment of the invention, the aforementioned arrangement of a pressure conduit, a chamber with different projected surface areas, and a change-energizing conduit is provided in duplicate form, i.e., for effecting changes either towards xe2x80x9coverdrivexe2x80x9d or xe2x80x9cunderdrivexe2x80x9d, respectively.
According to a particularly preferred embodiment of the invention, chambers of the kind described above, i.e., chambers with different projected surface areas in opposite piston travel directions, are supplied through different terminals with different pressure levels, with the pressure that determines the net piston force being present at one of the terminals. It is to be noted that the different pressure levels can occur, e.g., as a consequence of a throttle device, particularly one that can be set at variable levels.
In accordance with a particularly preferred embodiment of the invention, there is a relationship of mutual dependency between the force that acts on the piston device as a result of the different projected surface areas and a throttling device with a controllable variable passage cross-section that is arranged between a pressure-supplying conduit and a change-energizing conduit for changing the transmission ratio. Thus, the inventive concept provides in particular that for a given throttle cross-section, a force establishes itself on the piston device because of the difference in the projected surface areas and that this, in turn, causes a change of the throttle cross-section. Now, the change of the throttle cross-section leads to a pressure change on the projected surface areas which, again in turn, changes the throttle cross-section, and so on. In this manner, the system is regulated to settle into a certain piston position, particularly when aided by the supplemental effects of a spring force, a control-pressure force, and/or by providing a second device with a chamber with different projected surface areas.
In accordance with a particularly preferred embodiment of the invention, the continuously variable transmission is a conical-disk transmission with an endless flexible torque-transmitting device.
A conical-disk transmission with an endless flexible torque-transmitting device preferably comprises two pairs of disks, one of which is essentially locked to a rotatory input and the other to a rotatory output at least part of the time. Preferably, each of these (conical) disk pairs has an axially movable and an axially fixed disk-like part. An endless flexible torque-transmitting device such as a chain engages in particular the surfaces of the disk-like parts that face each other, whereby a torque can be transmitted from one disk pair to the other. Preferably, the chain has transverse bolts that bear against the tapered surfaces of the conical disks so that the friction force allows a torque to be transmitted. Because of the defined contact length between the conical disks and the chain, the friction force between the endless flexible torque-transmitting device and the disk pairs can be regulated and controlled through the amount of contact pressure force that is applied to the pairs of conical disks.
To effect a change of the transmission ratio, the conical disk pairs or, more precisely, the spacing of the disks of a pair in relation to each other, can be changed in a manner that is coordinated between the disk pairs. At least one actuator member is provided for this purpose, preferably of an at least partially hydraulic type and comprising at least one valve device of the kind described above.
According to a particularly preferred embodiment of the invention, at least one pressure chamber is arranged on at least one, but preferably on all, of the movable disks for the purpose of changing and/or maintaining the axial position of the movable disk. Essentially, the chamber adjoins the movable disk.
It is also particularly preferred if at least two hydraulic chambers are arranged at each axially movable disk, either in a parallel and/or a serial arrangement.
In a preferred arrangement, at least one of the chambers serves to set the ratio of the transmission. It is also preferred, if at least one of the chambers is used to maintain the transmission at a set ratio. In a particularly preferred embodiment of the invention, a torque sensor is arranged on the input shaft of the transmission. Preferably, the torque sensor converts a torque that is carried by a shaft, particularly an input shaft, into a corresponding amount of pressure. The preferred arrangement to accomplish this purpose is for the torque sensor to comprise at least two elements that are movable in relation to each other and for at least one of the elements to comprise a cam disk. Preferably, the cam disk is mounted in an axially fixed condition but has at least a limited degree of rotational freedom. The one or two cam disks have at least one tapered ramp. Arranged between the two parts or, more precisely, between the tapered ramps, is a space-holding body in the form of, e.g., a ball or a roller. When the two parts rotate in relation to each other, the space-holding body, e.g., the ball, runs along the tapered ramp and thereby changes the spacing of the two parts from each other. The traveling part in this arrangement belongs to a pressure chamber whose volume is decreased or increased by the axial travel of the part. Consequently, the volume change gives rise to a pressure change of a medium contained in the chamber.
In accordance with a particularly preferred embodiment of the invention, it is possible to connect the pressure chamber of the torque sensor at least partially to an outlet channel. It is especially preferred to insert a controllable throttle in the path of an outlet channel leading at least partially into the pressure chamber of the torque sensor. In accordance with a particularly preferred embodiment of the invention, the effective throttle cross-section of this throttle is dependent on the pressure level in the pressure chamber of the torque sensor and/or it is dependent on the torque acting on the torque sensor.
The object of the invention can also be achieved through a method in which a motor vehicle with a continuously variable transmission is operated in accordance with the following steps: First, at least one target value is set for a transmission ratio and/or a pressure level. Next, at least one actual value is determined for the target parameter, the actual value is compared against the target value and, if a difference is found between actual and target value, a correction is made to bring the respective parameter in line with the set target.
In a particularly preferred form of the method, at least two target values are set for transmission ratios and/or pressure levels of the continuously variable transmission.
The novel features which are considered as characteristic of the invention are set fourth in particular in the appended claims. The improved apparatus itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawing.